Trier, with its rich history dating back to Roman times, is home to some of the most impressive ancient structures in Germany. The Porta Nigra, a large Roman city gate, stands as a testament to the city's past and is a UNESCO World Heritage Site along with the Cathedral of St. Peter and the Church of Our Lady. Another remarkable structure is the Aula Palatina, also known as the Basilica of Constantine, which was built in the early 4th century and is notable for its immense size and the role it played during the reign of Constantine the Great. These historical monuments highlight Trier's significance as a former Roman capital and its continuous habitation since its foundation.